Biochemistry of acetic acid bacteria (AAB). Bacteria cope with life in harsh environments using specific stress responses and chemical alterations of cell components. The naturally acid-resistant AAB Acetobacter aceti has the ability to survive in molar concentrations of acetic acid at low pH. Most AAB are benign plant-associated organisms. Some strains produce huge amounts of acetic acid by oxidizing ethanol and have been used for millennia to make vinegar. These conditions poison other microbes, nearly all of which (unlike A. aceti) are unable to tolerate an acidic cytoplasm. We use this food-grade organism to explore bacterial acid survival strategies, which are among the most complicated stress responses deployed by microbes, including many pathogenic organisms. Our interests are centered on the adaptation of enzyme function and metabolism to acidic conditions. X-ray crystallographic studies of A. aceti proteins have revealed distinctive architectural features that are correlated with increased acid stability of pure proteins.

Enzyme mechanism. Enzymes are the gold standard for synthetic chemistry. We are particularly interested in those that form carbon-carbon bonds, among them the purine biosynthesis enzyme PurE and the citric acid cycle enzyme citrate synthase. An example of this remarkable chemistry is the carbon dioxide migration performed by PurE (illustrated above for the microbial form of PurE). Structural, mutagenesis, and pre-steady state kinetics methods are enlisted to understand how these enzymes do their jobs. We typically use enzymes from A. aceti in these studies because they are durable and cooperative.